The spout and showerhead are both open to the atmosphere, meaning that when the valve is on the water could travel either out the spout or up through the shower head. Because the spout is a shorter distance and at a lower elevation than the showerhead, water takes the path of least resistance out through the spout. When you pull up on the slider, the cup blocks the water from going to the spout, so the only way to go is through the showerhead. The pressure of the water holds the cup in place. The hole was possibly this manufacturer's method of relieving the pressure in the riser when the valve is off allowing the diverter slider to return to open. Answer from Genericname187329465 on reddit.com
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PlumbingSupply.com
plumbingsupply.com › home › diy plumbing tutorials › tub spouts index › how to choose & replace a tub spout
Learn how to remove and install various tub spouts
October 2, 2013 - Learn the differences between tub spout types, how to determine which style you have, and how to replace one.
Discussions

How does a tub diverter spout send water up to the shower?
The spout and showerhead are both open to the atmosphere, meaning that when the valve is on the water could travel either out the spout or up through the shower head. Because the spout is a shorter distance and at a lower elevation than the showerhead, water takes the path of least resistance out through the spout. When you pull up on the slider, the cup blocks the water from going to the spout, so the only way to go is through the showerhead. The pressure of the water holds the cup in place. The hole was possibly this manufacturer's method of relieving the pressure in the riser when the valve is off allowing the diverter slider to return to open. More on reddit.com
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December 11, 2022
plumbing - Bath tub spout rough in - Home Improvement Stack Exchange
I am surprised it is so hard to find a diagram or description of the proper way to rough in a bathtub spout. In case it makes any difference, the specific spout will be a Toto TS210EV with diverte... More on diy.stackexchange.com
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April 7, 2014
What causes the water to come out of the tub spout like this when the shower is on? And is it an easy fix for someone who is plumbing clueless? Thanks
Those spouts are either twist off, or there is a set screw. If it is a twist off, then you simply turn it counterclockwise to remove it. If there is a set screw, it is located close to the tub wall on the bottom of the spout. Most likely an allen key will be need to loosen the set screw, then you simply pull it off. Once you do get it off, soak it in some CLR and it'll be good as new. More on reddit.com
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May 31, 2023
converting tub spout diverter to handle diverter
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September 22, 2020
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Moen Solutions
solutions.moen.com › article library
Replacing a Tub Spout Diverter Gate - Moen Solutions
April 15, 2025 - A guide with instructions for replacing a tub spout diverter gate kit.
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Pinterest
pinterest.com › explore › home decor
Bathroom Faucet And Shower Diagram
February 8, 2013 - This is the most complicated of the installation diagrams. The shower valve has a diverter to take the water from the tub spout to the shower head. (If you have the water delivered to the tub spout first, it is easier to test the temperature.)
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Reddit
reddit.com › r/plumbing › how does a tub diverter spout send water up to the shower?
r/Plumbing on Reddit: How does a tub diverter spout send water up to the shower?
December 11, 2022 -

How does it work? The slider rides very loosely. The slider has a recess that captures a rubber "cup" the cup has a hole in it. Why does the slider and cup get pulled against the spout bulkhead rather than be pushed away? Is there a moving part in the rough-in that moves and directs water up to the shower when I pull up the diverter handle.

My spout was letting too much water dribble/leak out when the slider was up and water was diverted up to the shower. My repair was to place an o-ring inside the cup. The spout still dribbles, but much less.

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Allora USA
allorausa.com › home › blogs › blogs
Complete Guide to Shower Diverters: Types, Functions, and Installation Tips
April 16, 2025 - Pushing the knob back down allows water to flow freely into the tub again. It’s called a "tee" diverter because the plumbing forms a T-shape—one input (from the valve), with two outputs (showerhead and tub spout).
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DIY Home Improvement
diychatroom.com › home › forums › home improvement › plumbing
How does a shower spout diverter work? | DIY Home Improvement Forum
March 21, 2018 - For theoretical understanding, if the tub spout and showerhead were on the same horizontal/height, the water would still choose the path of least resistance and exit the tub spout. When you pull up on tub spout and divert water to the showerhead, you change the path of least resistance from the tub spout to the showerhead.
Find elsewhere
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The Home Depot
homedepot.com › diy projects & ideas › home decor ideas › bathroom ideas & projects
How to Install a Tub Spout - The Home Depot
September 7, 2023 - Whether you’re adding a new tub spout, or just replacing an old one, this is a simple home improvement project that requires only a few tools and materials, and is fairly easy to complete. ... Identify whether your bathtub spout has a shower diverter valve (L) or does not (R) and be sure ...
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Engineer Fix
engineerfix.com › how-a-tub-spout-diverter-works-with-diagram
How a Tub Spout Diverter Works (With Diagram) - Engineer Fix
November 13, 2025 - Learn how the tub spout diverter seals and redirects water. Detailed diagrams explain the mechanism, different styles, and fixes for common leaks.
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Master Plumber®
masterplumber.ca › home › support › how to instructions › shower & bath
Shower & Bath - Master Plumber®
March 23, 2023 - Replacing tub spout · Repairing ... · Tub-shower diverters · Replacing Tub Spout Section Link · Insert the handle of a hammer or suitable prying device into the spout opening and turn counter-clockwise....
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Physics Forums
physicsforums.com › classical physics
How does a bathtub/shower diverter valve work? • Physics Forums
November 6, 2022 - How does the tub diverter work. Obviously, if the tub faucet is blocked, the water will be pushed up to the shower head but initially, it seems to me that water will try to come from both the shower head and the tub faucet. What is going on here? The diameter of the spout downstream of the ...
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KOHLER
kohler.com › en › products › bathtubs › shop-bathtub-faucets › antique-standard-4-7-8-diverter-bath-spout-6855
Standard Diverter Bath Spout | K-6855 | KOHLER
Antique 4-7/8" diverter bath spout
The K-6855 bath spout with NPT connection offers a versatile, classic design. It features a wall-mount installation.
Price   $164.36
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Delta Faucet
deltafaucet.com › service-parts › find-parts-and-identify-product
Find Parts and Identify Your Product | Delta Faucet
Solves drips from the outlet when water is off or leaks behind the handle View Tub/Shower Cartridges ... Answer step-by-step questions to narrow down the results to your product model number resulting in a link to the product detail page containing a list of parts and a parts diagram.
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GROHE
grohe.us › home › diverter tub spout
Diverter Tub Spout
Following are the list of products or parts which you can also add to your list along with the product You can also download the parts diagram by clicking on the <strong>Download Repair Parts Diagram button</strong>
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Danco
danco.com › home › how to repair a tub spout
Repair Leaking Tub Spout Diverter Pull in Shower Mode - Danco
December 17, 2021 - While many diverters utilize a pin knob on the tub spout that must be pulled, there are many varieties on a 2-3 handle tub/shower that use a button or an additional handle located between the hot and cold knobs.
Top answer
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According to the installation manual for the spout, the nipple for the spout should be installed a min of 3/8" to a max of 3/4" past the finished wall. There is a pipe adapter that you screw onto the nipple. The spout slides over this adaptor and is set in place with a set screw located on the bottom. This allows for the correct orientation of the spout.

The hole for the spout through the tile and back board should be about 1/4" to 1/2" larger than the nipple diameter allowing for an 1/8" to 1/4" gap between the nipple and the tile.

There should be installation instructions for the diverter valve that will include the vertical location of the valve relative to the spout, as well as the set back distance in the wall. There is usually a plastic over on the diverter valve that is to be set flush with the finished wall. This cover also provides the opening required for the valve. Check the diverter valve instructions.

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Use a DROP-EAR elbow and provide some framing to screw it to, please.

How far past the tile surface - how deep is the spout when you get to threads? 1/2" US pipe thread is supposed to be tight when engaged 1/2", so add 1/2" to that. To provide room for another turn if needed and caulking, perhaps another 1/8" beyond THAT.

How small the hole - I like just big enough for the pipe, acceptable ranges from there up to just smaller than the back of the spout. Just enough for the pipe (or within 1/8") allows you to double up on caulking - caulk the hole around the pipe AND caulk the back of the spout (but leave a gap/weep hole under the bottom of the spout) - if there is a shower, this area is a prime one for leaks, so sealing it well is good.

How to get the spout vertical? As with anything else involving pipe threads and alignment, by judging whether you can get one more turn or not every time it's vertical, and stopping when you don't think you can. If you mis-judge, take it off, redope, and try again. IME, teflon dope beats teflon tape here...

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Mr. Rooter
mrrooter.com › home › about/blog › how does a shower diverter work
How Does a Shower Diverter Work? | Mr. Rooter Plumbing
Three-valve shower diverter: Tubs ... directly to a showerhead. Turning its third handle clockwise 180 degrees will do that job, while turning it the opposite way will restore flow from the tub spout....
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Moen Solutions
solutions.moen.com › article library
Types of Tub Spouts - Moen Solutions
March 31, 2023 - This article will explain how to identify a Moen tub spout by function, material, length and how it is secured to the wall.
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This Old House
thisoldhouse.com › this old house › bathrooms
How To Repair a Shower Diverter
April 18, 2024 - A lever on the tub spout controls water flow. Two-valve diverter: This setup has one knob for water temperature and another that acts as the shower diverter.